Disable unused Python 2 variant. am: f3568df232

Original change: https://android-review.googlesource.com/c/platform/external/python/google-auth-library-python/+/2221605

Change-Id: If3b5ec2dad863c446eede8de170dc3ed29eb25a3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>